Non-activated Samples Research Articles

Activation of nickel foam, as a current collector of a supercapacitor, by impact nickel plating: influence of treatment conditions

Nickel foam is widely used as a current lead/current collector and as the base of nickel hydroxide electrodes for hybrid supercapacitors. An investigation of the influence of activation conditions for a commercial sample of nickel foam produced by Linyi Gelon LIB Co Ltd (China) was carried out using the method of impact nickel plating. The morphology of activated and non-activated nickel foam samples was investigated by scanning electron microscopy. Activated and non-activated nickel foam samples were investigated by methods of cyclic voltammetry and galvanostatic charge-discharge cycling in the supercapacitor mode. It was shown that upon activation at i=1 A/dm2 and τ=10 min, a thin layer of porous nickel with incomplete coverage was formed. Activation with impact nickel at i=7 A/dm2 and τ=3 min revealed the formation of a nickel coating with a highly developed surface, on which local cracks were found as a result of the accumulation of internal stresses. Activation with impact nickel at i=1 A/dm2 and τ=10 min led to the formation of a coating with a highly developed surface, with significant peeling of the coating. Cyclic voltammetry showed high efficiency of impact nickel activation at i=7 A/dm2, τ=3 min, and i=20 A/dm2, τ=5 min. The specific current of the cathode peak increased 6.06–6.44 times with respect to the non-activated sample. The investigation of the activated samples' electrochemical characteristics by the galvanostatic cycling method showed that impact nickel activation at i=1 A/dm2 and τ=10 min was insufficient. It was found that at a discharge up to E=0 V, the maximum specific capacitance of 0.731 F/cm2 was obtained for samples activated by impact nickel at i=7 A/dm2 and τ=3 min. The increase in specific capacitance compared to the non-activated sample was 4.49 times. At full discharge, the highest electrochemical activity was found for nickel foam samples activated by impact nickel at i=20 A/dm2 and τ=5 min. The specific capacitance was 0.505 mA∙h/cm2, and it increased 9.02 times

Effect of mechanical activation on the hypochlorite leaching of Sarcheshmeh molybdenite concentrate

ABSTRACT Hydrometallurgical extraction of molybdenum from sulfidic molybdenite concentrates is an important issue from technical, economic, and environmental viewpoints. The influence of mechanical activation on the hypochlorite leaching of a molybdenite concentrate (Kerman, Iran) were studied in a stirred reactor at batch mode. The effects of several critical parameters, including pH, temperature, reaction time, NaClO concentration, and liquid to solid (L/S) ratio on the rate and extent of molybdenum extraction from the concentrate were investigated. Maximum molybdenum extractions, 98% and 95%, obtained for the mechanically activated and nonactivated concentrates, respectively after 60 min at 50°C, stirring speed of 500 rpm, L/S of 333 mL/g, pH of 9, and using 40% NaClO solution. Specific surface area and particles size measurements in conjunction with FE-SEM images showed that improvement in the extraction after mechanical activation could be due to increasing the surface area and changing the crystal structure of the concentrate. Mechanical activation had a significant effect on molybdenum extraction after 2 min, (13% difference in extraction); however, after 60 min, molybdenum extractions from mechanically activated and nonactivated samples were 97% and 92%, respectively. It was found that mechanical activation has a significant effect on the leaching of molybdenite in short reaction times.

Mechanical activation modes of chalcopyrite concentrate and relationship between microstructure and leaching efficiency

In this study, a high-energy planetary mill was used to perform mechanical activation of chalcopyrite in dry-, moist-, and wet-milling modes. Granulometric and microstructural changes of chalcopyrite were characterized, and their effects on Cu dissolution were distinguished. Although water was added during milling to reduce agglomeration, it led to the inhibition of energy transmission. The maximum Brunauer–Emmett–Teller surface area of 8.382 m2/g was obtained in samples subjected to 7 h of moist milling. Dry milling resulted in considerable microstructural changes; the amorphization degree, grain size, and lattice strain of the chalcopyrite were 66.4%, 10 nm, and 0.427 × 10−2, respectively. Samples that had undergone 7 h of dry milling exhibited the highest copper extraction efficiency of 48.9%, which was 81.5 times higher than that for the nonactivated samples. The results of kinetics analysis revealed that the degree of amorphization exhibited a greater reactivity of chalcopyrite than the surface area did, and the enhancement in the leaching efficiency was highly consistent with the mechanical activation parameter. In addition, because of the selective rupturing of the chalcopyrite lattice, a “sulfur channel” appeared on the surface of the dry- and moist-milling samples, which proved that passivation decreased and leaching was enhanced. The results of this study can provide considerable insight on chalcopyrite leaching.

Comparative investigation of different types of nickel foam samples for application in supercapacitors and other electrochemical devices

Nickel foam is widely used as a current lead/current collector and the basis of nickel hydroxide electrodes for various electrochemical devices – batteries, hybrid supercapacitors, devices for electrocatalytic oxidation of organic substances. The characteristics of commercial samples of nickel foam produced by Novomet-Perm (Russian Federation) obtained by electroless and then electrochemical nickel plating and Linyi Gelon LIB Co Ltd (China) obtained by electroless nickel plating were studied. The nature of passivity was determined by forming model samples of electrochemical and electroless nickel on a steel base. For the passive sample, activation was carried out by applying a layer of electrochemical nickel from an impact nickel plating solution. Activated, non-activated samples of nickel foam, as well as model samples, were studied by the methods of cyclic voltammetry and galvanostatic charge-discharge cycling in the supercapacitor mode. Comparative analysis of Chinese-made and Russian-made nickel foam samples showed significant passivity of the former – in cyclic voltammetry, the activity was 4.8 times lower, with galvanostatic charge-discharge cycling – 2.59 times lower. It was suggested that high passivity was determined by the fact that the sample consisted of Ni-P or Ni-B alloy. This assumption was proved by the method of natural simulation. The electrochemical activity of electroless nickel was 1.25 times lower than that of electrochemical nickel (according to cyclic voltammetry data) and 1.58 times lower (according to galvanostatic cycling data). For the first time, Chinese-made nickel foam (electroless nickel) was activated by applying a layer of electrochemical nickel from an impact nickel electrolyte. The high activation efficiency was shown as follows – on the cyclic curve, the specific current of the anodic peak increased 8.71 times, and with galvanostatic cycling, the increase in specific capacity was from 1.73 times (at i=120 mA/cm2) to 4.84 times (at i=20 mA/cm2)

Effect of microwave radiation and mechanical activation on the Carbothermic reduction of molybdenum trioxide: Improving the practical efficiency

In this research two different paths were used to cabothermic reduction of MoO3. In the first and second path, as received MoO3 and graphite with stoichiometric ratios were mixed and mechanically activated at 5, 10, 15 and 24 h and heating by microwave oven (first path) and furnace at 700 and 1000 °C in second path. The XRD results of activated samples before heating showed that, MoO2 was produced in the planetary ball mill after 5 h milling and don't change to another phase during milling up to 24 h. the SEM and XRD results in first and second path showed that the final product was molybdenum carbide but in the non-activated samples the final products were molybdenum carbide and unreacted MoO2. The practical efficiency calculations in first and second method showed that heating of samples by microwave radiation and mechanical activation increase the practical efficiency and decrease the sublimation of molybdenum trioxide. The TGA analysis of non-activated MoO3+ C mixture indicated that the reduction goes with three steps but in the 24 h activated sample, it was seen that the reduction goes with one peak. In other words, the first and second peaks in non-activated sample were not detected in the activated sample that increases the practical efficiency due to prevent the sublimation of MoO3

MCS Hypershear Modulates Platelet Membrane Fluidity, Lipid Species, and is Gender Specific

Shear-mediated platelet activation (SMPA) is a main driver of MCS thrombosis. A target of MCS shear, driving activation, is the platelet membrane - leading to potential alteration of biophysical properties. Here, we examined the effect of shear stress-accumulation on platelet membrane fluidity and on platelet lipid species profile - both retained (membrane) and free (ejected) post-activation. Human gel-filtered platelets (20,000 plts/uL) were exposed to shear in a hemodynamic shearing device (70 dynes/cm2 x 10'); or to thrombin (1U/mL x 10') as a chemical agonist comparator. Membrane fluidity was determined by ໿fluorescence anisotropy of the probe TMA-DPH (1uM, 5' @ 37C). Platelet lipids - both retained (cellular) and free (ejected) following activation - were extracted and analyzed via high resolution liquid-chromatography tandem mass spectrometry (LC-MS/MS). Shear stress accumulation increases platelet membrane fluidity - with a 6% increase noted even for the brief shear exposure examined. Shear stress exposure results in significant alteration of overall platelet lipid composition, with increase in supernatant lipid species relative to the non-activated samples such that 72% of identified lipid species have >2-fold increase. Lipid species altered in the supernatant of sheared platelets were unaltered under thrombin treatment. Interestingly, within the limits of our analysis, a gender-based difference in retained lipid species was seen with shear but not with thrombin activation. Male donors showed at least a 2-fold decrease in 53% of lipids identified in the pellet of the sheared platelets using negative mode MS. In contrast, female donors had only 6% of lipids decrease >2-fold relative to non-activated platelets, while 77% of lipids showed a less than 2-fold change in either direction. Shear stress has a specific impact on platelet membranes - leading to an increase in fluidity, and alteration of platelet lipidomic profile, which differs from biochemical activation, with evident gender-based differences. Specifically, shear leads to an increase in the number of lipids ejected across all donors, and a male-preferred decrease in retained lipid species. This sex-based difference in platelet composition resulting from shear exposure raises the issue of altered responsiveness that may impart gender differences in in MCS outcomes.

Optimal activation methods for maximizing the concentrations of platelet-derived growth factor-BB and transforming growth factor-β1 in equine platelet-rich plasma.

Platelet-rich plasma (PRP) therapy has been widely applied in various medical fields including humans and horses. This study aimed to establish an optimal activation method to stably and reproducibly maximize the concentrations of platelet-derived growth factor-BB (PDGF-BB) and transforming growth factor-β1 (TGF-β1) contained in equine PRP. Autologous PRP was prepared from 11 Thoroughbreds. For the activation test, PRP was activated by either a single freeze-thaw cycle (Fr) or adding calcium and autologous serum containing thrombin (Ca). PDGF-BB and TGF-β1 concentrations in Fr, Ca, nonactivated (No), and platelet-poor plasma (PPP) samples were determined using ELISA and compared. For repetitive freeze-thaw test, PRP was subjected to single (Fr1), double (Fr2), triple (Fr3), or quadruple (Fr4) freeze-thaw cycles and the concentrations of both growth factors in samples were compared similarly. The PDGF-BB concentration in Ca was significantly higher than that in other preparations. The TGF-β1 concentrations in Fr and Ca were significantly higher than those in PPP and No, with no significant differences between Fr and Ca. The concentrations of both factors were significantly increased in PRP treated with multiple cycles of freeze-thaw compared with that in PRP treated with a single cycle. No significant differences were noted among Fr2, Fr3, and Fr4. Our findings suggest that activation by adding calcium and autologous serum is optimal for instant use of PRP and that double freeze-thawing is an easier and optimal activation method for cryopreserved PRP.

Formation kinetics and cation inversion in mechanically activated MgAl2O4 spinel ceramics

Solid-state mechanical activation of MgO and α-Al2O3 powders was used to produce MgAl2O4. The cation site occupancy in the resulting MgAl2O4 spinel was investigated using different methods. Differential thermal analysis and thermal gravimetry showed that mechanical activation reduced the spinel formation temperature by around 200 °C, and the corresponding activation energy by about 25%. In addition, characteristic temperatures for evaporation of physisorbed water and decomposition of Mg(OH)2 shifted to lower values, and peaks were more pronounced. Raman spectra were used to characterize the degree of inversion as a function of the sintering temperature for all of the sintered specimens, indicating that the breaking point for ordering of the crystal structure was around 1500 °C for non-activated samples, and 1400 °C for activated samples.

Activation of Carbon Nanofibers and Their Application as Electrode Materials for Supercapacitors

Surface activation of carbon materials produced by chemical vapor deposition onto a nickel plate is described. The products of pyrolysis of a gas mixture composed of propane, butane, and isobutane were for the most part nanofibers. This material was used as the active mass for electrodes of supercapacitors. The elec¬trodes were activated with a potassium hydroxide (KOH) at temperatures of 700 and 800°C in the atmosphere of argon. The activation efficiency was evaluated by the capacitance of supercapacitor cells by measurement of the electrochemical properties based on activated and unactivated materials. The salt 1.1-dimethylpyrrolidinium tetrafluoroborate (DMP) in acetonitrile (AN) was used as an electrolyte. The specific surface area of the electrodes was determined from adsorption data. It was shown that the specific surface areas of non-activated samples and samples activated at 700 and 800°C were 190, 338, and 586 m2 g-1, respectively. The specific capacitance of the samples also became higher with increasing specific surface area.

Activated Luffa derived biowaste carbon for enhanced desalination performance in brackish water.

Membrane capacitive deionization (MCDI) is an effective process to remove salt ions from brackish water. In this work, a systematic investigation was carried out to study the effects of applied potential and salt concentration on salt adsorption capacity (SAC), charge efficiency (Λ) and energy consumption in an MCDI system using Luffa biowaste derived carbon as electrodes. We studied the comparative MCDI performance of Luffa derived carbon as electrodes before and after activation. Furthermore, the desalination capacities of the electrodes were quantified by batch-mode experiments in a 2500 mg L−1 NaCl solution at 0.8–1.2 V. Activated Luffa carbon showed a high SAC of 38 mg g−1 at 1.2 V in a 2500 mg L−1 NaCl solution with a low energy consumption of 132 kJ mol−1 salt as compared to non-activated samples (22 mg g−1, 143 kJ mol−1). The adsorption mechanisms were investigated using kinetic models and isotherms under various applied potentials. Consequently, the excellent SAC of activated Luffa carbon can be attributed to the presence of micro/mesoporous network structure formed due to the activation process for the propagation of the salt ions.

CO2 gas-adsorption calorimetry applied to the study of chemically activated carbons

In this work, the microporous structure of a series of H3PO4 chemically activated carbons from peach stones with increased activation degree were investigated. CO2 Adsorption equilibrium isotherms and differential enthalpy curves were simultaneously measured at 300K using a Tian-Calvet microcalorimeter coupled to an adsorption manometric setup. Temperature programmed decomposition experiments were used to assess density of oxygen functional groups and determine the impact of surface chemistry on CO2 adsorption capacity. Computer based theoretical calculations were also performed to attempt to predict the adsorption enthalpy profiles. The most activated sample (Xp=0.90) has an average adsorption enthalpy which is approximately 8kJ/mol lower than that of the non-activated samples carbonized under the same conditions. The combination of techniques enabled a better understanding of the pore filling regimes with increasing coverage, since the use of CO2 as a probe gas allows accessing small pores, which otherwise would not be identified from N2 isotherms at 77K. The oxygen content on the carbon surface decreased almost 80% with the increasing degree of activation and did not influence in the CO2 adsorption. Besides providing information about carbon chemistry, CO2 adsorption calorimetry can also be successfully applied to the screening of carbons intended for CO2 capture.

Activation of the nickel foam as a current collector for application in supercapacitors

Nickel foam is widely used as a current collector and as a major component of the faradic electrode in supercapacitors. Activation of nickel foam would allow increasing the capacity of the nickel hydroxide electrode or preparing high-speed electrodes without additional active material. Multiple (1 – 20 times) short-term (5 min) treatment in a 1 М solution of HCl, H3BO3 or H2C2O4 has been proposed. The possibilities of activation of commercial nickel foam samples manufactured by “Novoment-Perm” (Russian Federation) and “Linyi Gelon LIB Co Ltd” (China) have been studied. Activated and non-activated nickel foam samples have been studied by means of X-ray diffraction analysis and scanning electron microscopy, electrochemical characteristics were determined by means of cyclic voltamperometry and galvanostatic charge-discharge cycling in the supercapacitor regime. The comparative analysis of nickel foam samples from Chinese and Russain manufacturers has revealed very low reactivity and low susceptibility to activation of nickel foam from Chinese manufacturer. An assumption has been made that low reactivity is because the sample is composed of Ni-P or Ni-B alloy. The maximum specific capacity of 0.084 F/cm2 has been obtained after 20 treatments in HCl solutions. The activation mechanism is the increase in the specific surface area of nickel. However, this value is significantly lower than that of non-activated nickel foam from Russian manufacturer (0.333 F/cm2). It has been discovered that the nickel foam sample from Russian manufacturer can be easily activated. The maximum activation effect is achieved when treated with oxalic acid: specific capacities are 1.213 F/cm2 (one treatment), 6.578 F/cm2 (five treatments) and 20.003 F/cm2 (twenty treatments). The activation mechanism is the formation of nickel oxalate on the surface of nickel foam. The results of the comparative analysis have revealed the effectiveness of activation of the nickel foam sample from Russian manufacturer by multiple short-term treatment with oxalic acid. It has been concluded that activation of the nickel foam sample from Chinese manufacturer by multiple short-term treatment in solutions of hydrochloric, boric and oxalic acids is ineffective. Activation of nickel foam from Chinese manufacturer requires the development of a different method.

Quantitative Characterization of Activated Carbon from Cow, Donkey, Chicken and Horse Bones from Ezzangbo in Ebonyi State, Nigeria

Animal bones have been used to produce carbon char for quality assessment of activated carbon over non activated carbon (used as sample control) as influenced by method of activations (acid and heat). In this study samples analyzed were carbonized in a closed crucible at 400°C and ground into powder after cooling. 200g of each of the crushed samples was activated using 250ml of 2 M Hydrochloric acid for one hour at 80°C and another 200g was activated by thermal method at 120°C for 3 hours. To obtain the optimum weight lost of the carbons, the carbonization period was varied from 0.5-3hours. From the result, increase in carbonization time caused an appreciable increase in the percentage weight loss, this reached a maximum value at a carbonization time of 2.5 hours for both carbon samples at a corresponding percentage weight lost of 63%, 58%, 54% and 62% for cow, donkey, chicken and horse bones respectively. The percentage of carbon yield of cow, donkey, chicken and horse bones upon acid activation are in increasing order of cow (48.92%) > horse (48.64%) > donkey (46.34%) > chicken (44.80%) bones and horse (37.03%) > cow (36.21) > donkey (34.96%) > chicken (30.18%) upon heat activation. Among the bone samples, chicken bone has the least ash content of 12.84%, 11.05% and 15.84% for acid, heat and non-activated samples respectively. The difference in bulk densities of acid activated and heat activated carbons are infinitesimal. The order of increasing bulk densities is cow (0.80g/m3) > donkey (0.78g/m3) = horse (0.78g/m3) > chicken (0.49g/m3). The heat activated carbons shows higher percentage of hardness than the acid activated and non-activated carbons. This study indicated that activated carbons from Cow, Donkey, Chicken and Horse are effective as adsorbents with those obtained from chicken having better features of adsorbents.

A STUDY ON THE PREPARATION AND ADSORPTION PROPERTIES OF ACTIVE CARBON FROM PEACH KERNEL

Peach Kernel (PK) is considered one from many agricultural wastes that represents negative impact on the environment. This work describes a method for the preparation of activated carbon from PK, converting its negative impact on the environment, to positive to be used for removal of contamination. The activated carbon (AC) was prepared in two separate steps of carbonization and activation at 550 & 600 oC. The physical activation was performed by water vapor. The mechanism of adsorption varies from physical and chemical adsorptions. The Fruendlich and Langmuir equations were determined. The yields of produced AC for PK samples were 36.82 % and 15.30 % at 550 oC and 650 oC respectively. Tests were made on prepared AC activated at 650 oC. The percentage moisture content varied from 2.94 – 3.72 %. The percentage volatile matter content varied from 42.51- 61.93 % for PK powder and granules respectively. The percentage ash content varied from 0.49 to 2.41%. The apparent density varied from 0.508 to 0.565 g/cm3. The pores volumes varied from 0.525 – 0.573 cm3/cm3. The iodine numbers for non-activated PK carbon samples were 254.80 - 344.90 for granules and powder respectively. The iodine numbers for activated PK carbon samples were 370.16 and 507.60 for granules and powder respectively. The surface areas by multi-point BET were 26.009 and 40.277 m2/g for non-activated and activated PK respectively. The SEM (Scanning Electron Microscope) images of PK AC show irregular spherical shapes with average diameter of (5-16) nm and macro pores with diameters of greater than 50 nm. The adsorption of iodine on PK AC followed both more Langmuir isotherm with R² = 0.9498 (a= 0.3877 & b= 0.3225) than Fruendlich with R² = 0.8419 with (n=1.4428 & k= 1.1951).

Effect of activation on the porous structure and the strain and strength properties of beech wood biocarbon

The effect of activation on the size, specific volume, and surface area of pores in a monolithic biomorphic material obtained by carbonization of beech wood is studied. It is shown that under optimal activation mode with a steam heated to 970°C, the total pore volume and surface, determined by adsorption curves, increased by 20 and 18 times, respectively. With the use of high-precision interferometric procedure, strain curves are obtained under uniaxial compression with a stepwise loading, and the strain rate is measured with a step of moving of 325 nm for activated and nonactivated samples. Despite an increase in porosity, the strength and maximum deformation of the samples do not decrease. The behavior of the strain rate jumps is analyzed in the micro- and nanometer range. It is shown that the maximum size of the micrometer jumps (4 μm) correlates well with the average size of the possible strain area in the samples (the average distance between the pores of small size), and the minimum dimensions of the strain jumps are close to the size of mesopores. Assessment of the strain change and its rate upon activation indicates that the effect of activation on the strain and strength characteristics is defined by nanometer defects, the most likely of which are microand mesopores.

The Phosphatase Inhibitor Calyculin-A Impairs Clot Retraction, Platelet Activation, and Thrombin Generation.

The aim of this study was to investigate the effect of the serine/threonine protein phosphatase inhibitor, calyculin-A (CLA), on clot formation and on the procoagulant activity of human platelets. Platelet-rich plasma (PRP) samples were preincubated with buffer or CLA and subsequently platelets were activated by the protease-activated receptor 1 (PAR-1) activator, thrombin receptor activating peptide (TRAP). Clot retraction was detected by observing clot morphology up to 1 hour, phosphatidylserine- (PS-) expression was studied by flow cytometry, and thrombin generation was measured by a fluorimetric assay. For the intracellular Ca2+ assay, platelets were loaded with calcium-indicator dyes and the measurements were carried out using a ratiometric method with real-time confocal microscopy. CLA preincubation inhibited clot retraction, PS-expression, and thrombin formation. TRAP activation elicited Ca2+ response and PS-expression in a subset of platelets. The activated PRP displayed significantly faster and enhanced thrombin generation compared to nonactivated samples. CLA pretreatment abrogated PS-exposure and clot retraction also in TRAP-activated samples. As a consequence of the inhibitory effect on calcium elevation and PS-expression, CLA significantly downregulated thrombin generation in PRP. Our results show that CLA pretreatment may be a useful tool to investigate platelet activation mechanisms that contribute to clot formation and thrombin generation.

Effects of freezing and activation on membrane quality and DNA damage in Xenopus tropicalis and Xenopus laevis spermatozoa.

There is growing concern over the effect of sperm cryopreservation on DNA integrity and the subsequent development of offspring generated from this cryopreserved material. In the present study, membrane integrity and DNA stability of Xenopus laevis and Xenopus tropicalis spermatozoa were evaluated in response to cryopreservation with or without activation, a process that happens upon exposure to water to spermatozoa of some aquatic species. A dye exclusion assay revealed that sperm plasma membrane integrity in both species decreased after freezing, more so for X. laevis than X. tropicalis spermatozoa. The sperm chromatin dispersion (SCD) test showed that for both X. tropicalis and X. laevis, activated frozen spermatozoa produced the highest levels of DNA fragmentation compared with all fresh samples and frozen non-activated samples (P<0.05). Understanding the nature of DNA and membrane damage that occurs in cryopreserved spermatozoa from Xenopus species represents the first step in exploiting these powerful model organisms to understand the developmental consequences of fertilising with cryopreservation-damaged spermatozoa.

Effects of Composition and Fe on the Liquid Phase Sintered W-Brass Composites

In this study, W-brass with the composition of tungsten (W) ranging from 50 – 70 wt. % and the balance is brass and other samples with 1 wt. % Fe activator added to the above W and brass composition were both liquid phase sintered at 11500C. The effects of composition and Fe activator on the densification, microstructure and hardness were investigated. As a result of Zn evaporation, compacts expansion, porosity and mutual insolubility between W andbrass, the sintered densities of all the samples were lower than their green densities. Though the Fe activated samples equally expanded, their relative sintered densities were higher than the non-activated samples. Optimum densification was obtained in the samples with 40 – 50 wt. % brass). The porosity in the sintered samples ranges from 24.09% - 27.51%. The hardness increases with the increase in the volume fraction of W. The general low hardness values are a direct consequence of low sintered densities.

Catalytic decomposition of biomass tars: The impact of wood char surface characteristics on the catalytic performance for naphthalene removal

Catalytic decomposition of naphthalene over four different wood chars has been investigated. The effect of the pyrolysis temperature and activation with CO2 on the char structure and catalytic activity of the wood char has been studied in order to elucidate the tar decomposition rate and char stability towards deactivation. The wood char catalysts were produced by pyrolyzing spruce wood chips in a tubular batch reactor at 500 and 800°C. Part of both char samples was further activated by purging CO2 through a bed of the pyrolysis char at 800°C. The wood char reactivity for naphthalene cracking was investigated using a fixed bed quartz reactor in a heated furnace with a constant inlet gas flow of naphthalene. Thermal decomposition was evaluated at temperatures between 700 and 1050°C and taken into account when assessing the catalytic activity of each wood char at 850 and 1050°C. The structural features of the char catalyst were examined before and after the tar cracking experiment by CO2 and N2 adsorption technique as well as scanning electron microscopy (SEM). Catalytic deactivation was studied by analyzing the surface structure of the char samples over exposure time to naphthalene. The self produced wood char samples were compared to a commercial activated carbon to classify their structural and catalytic properties.Catalytic tar cracking tests with all wood char catalysts confirmed that the activated char samples showed a high catalytic activity for naphthalene decomposition into carbon and hydrogen, whereas the non-activated char samples did not enhance the tar cracking reaction at 850°C significantly.N2 adsorption revealed that deactivation of the char catalyst happens mainly due to coke deposition blocking the char active sites. The time evolution of the wood char's tar cracking activity was found to be proportional to the amount of micropores with a pore diameter smaller than 0.7nm. SEM measurements visualized structural changes on the macroscopic char surface caused by naphthalene decomposition under an inert nitrogen atmosphere.

SHS in the Ni–Al system: Influence of mechanical activation, vacuum heat treatment, and ambient pressure

Explored was the influence of mechanical activation (MA), vacuum heat treatment (VHT), and ambient pressure on combustion of Ni–Al mixtures. Burning velocity was found to grow with increasing MA time. An increase in ambient pressure hampered the elongation of burned samples. No elongation was found for non-activated and heat-treated samples. VHT strongly accelerated combustion and prevented the formation of cracks on the surface of burned samples. The results were rationalized in terms of convection–conduction combustion theory.